Mobility of Nitrogen‐15‐Labeled Nitrate and Sulfur‐34‐Labeled Sulfate during Snowmelt
Bibliographic record
Abstract
The objective of this study was to investigate the winter dynamics of SO 4 2− and NO 3 − in a forested soil to better understand controls on these acidifying anions during snowmelt. In February 2004, a stable isotopic tracer solution with 93 atom% 34 S as H 2 34 SO 4 and 99 atom% 15 N as NH 4 15 NO 3 was applied to the snowpack at the Hubbard Brook Experimental Forest in New Hampshire. The chemical and isotopic compositions of throughfall, snow, snowmelt, and forest floor leachates were monitored for 10 mo following the addition of the tracers. The 34 SO 4 2− and 15 NO 3 − tracer amounts in forest floor leachates were highest in the first fractions of meltwater and declined exponentially until returning to ambient levels in mid‐May. Isotopic mass balances indicated that SO 4 2− and NO 3 − were conservative in the snowpack, with tracer recoveries near 100%. In contrast, only 54 to 62% of the 34 SO 4 2− and 49 to 58% of the 15 NO 3 − were recovered in forest floor leachates, suggesting that much of the SO 4 2− and NO 3 − that infiltrated the forest floor during snowmelt was retained or transformed. Microbial biomass δ 15 N values in the forest floor remained low during snowmelt and the natural abundance values of δ 18 O–NO 3 − in forest floor leachates were indicative of an atmospheric rather than a microbial source. These results suggest that, in this study, microbial immobilization and subsequent mineralization and nitrification of snowpack NO 3 − was insignificant in the forest floor during snowmelt.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".